Directive antenna system



Sept. 20, 1949. c c CUTLER v DIRECTIVE ANTENNA SYSTEM 5 Sheets-Sheet 1 Filed July 21., 1945 TRANSLATION DEVICE TRANSLA TION DEVICE INVENTOR By OCCUTLER v TRANSLATION ATTORNEV Sept. 20, 1949. Q C, CUTLER DIRECTI VE ANTENNA SYSTEM 5 Sheets-Sheet 2 Filed July 21, 1945 W w s R a 3 m w TV C .6 mm M EM F Wm rP m w M m w w. E H a w r u. a a 0 0 0 0 0 0 0 0 0 3\ v 0 0 0 O 0 0 0 0 0 w w M m m a a 4 2 2 4 6 a w w M w w v kotuwmfimxqawz lNl/ENTOR C. C. CUTLER A TTOR/VEV Sept. 20, 1949.

Filed July 21, 1945 ANGULAR DIRECTION c. c. CUTLER 2,482,158

DI RECTIVE ANTENNA SYSTEM 5 Sheets-Sheet 3 FIG. 4

DIRECTIVE PATTERNS SKSTEM or INVENTION (FIG. mm DRUM m/mm/vn-NNA RELATIVE FIELD STRENGTH- DEC/EELS 6.4 IN: 3/. 3 DEKIYIBELS V E N TOR V (1%. CUTLER A TTOPNE V Sept. 20, 1949.

Filed July 21, 1945 c. c. CUTLER 2,482,158

DIRECTIVE ANTENNA SYSTEM 5 Sheets-Sheet 5 FIG. 7

DIRECTIVE PAT TERNS SYSTEM OFPRIOR ART WITH I DISK PRIMARY ANTENNA RELATIVE FIELD STRENGTH-DECIBELS GAIN: 30.8 DEC/EELS ANGULAR eDIRECTIOIV OCCUTLER ATTORNEY Patented Sept. 2Q, 1949 DIRECTIVE ANTENNA SYSTEM Cassius C. Cutler, Oakhurst, N. 3., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July 21, 1945, Serial No. 606,426 3 Claims. (01. 250-3355) This invention relates to antenna systems and particularly to microwave directive antenna sysems.

As is known, highly directive point-beam antenna systems comprising a conventional paraboloidal reflector and a front or rear feed of the dielectric guide type have been suggested for use in the microwave field and in particular in the microwave radio detecting and ranging or socalled radar field. For example, Figs. 1 and 2 of my copending application, Serial No. 518,377, filed January 15, 1944, now Patent No. 2,422,184, issued June 17, 1947, illustrate a prior art pointbeam antenna system comprising a main conventional paraboloidal reflector, a dielectric guide extending through the reflector vertex to the reflector focus and having at its end a primary antenna aperture, and a front disk reflector facing the aforementioned aperture'and the main reflector. While, in general, the prior art systems, including the one just described, are being used with success, the results secured are by no means entirely satisfactory, principally because the electric or E plane and the magnetic or H plane major lobe patterns are substantially different in shape and, in both planes, pronounced or relatively strong minor lobes are obtained. The difference in the shapes of the twopatterns, and'the relatively large intensity of the minor lobes, may be ascribed to the fact that the primary antenna aperture does not transceive a perfectly spherical wave front or, stated diiferently, does not sufficiently approximate or simulate the ideal point source or point receiver for a paraboloidal reflector. As is well understood, especially in the optical art, a paraboloidal reflector converts a spherical Wave front originating at its point focus into a plane or flat wave front perpendicular to the reflector axis and, conversely, transforms an incoming plane wave front into a spherical wave front centered on the focus. If the active or primary antenna element at the point focus is not dimensionless, a perfectly flat wave front is not established in the case of transmission and, in reception, the spherical wave front incoming to the primary antenna is not absorbed in an optimum manner, that is, maximum directive action in transmission, and in reception are not obtained. Considered in terms of optics, under the-condi ion. s u ed a o e, undesi ed aberration occurs and the system is, strictly speaking, not aplanatic. Accordingly, it appears desirable to obtain a paraboloidal antenna reflector system which substantially avoids the detrimental operational effects inherent in conventional prior art reflector systems and which, in addition, possesses distinct advantages over the reflector systems heretofore suggested.

It is one object of this invention to transmit or receive a maximum amount of radiant energy along a given path or direction.

It is a further object of this invention to obtain, in a point-beam directive antenna system, a directive characteristic which is symmetrical about the axis or direction of maximum action.

i It is another. object of this invention tosecure, in a point-beam directive antenna system, E and H plane major lobe patterns having the same shape. r

It is another object of this invention to obtain, in a point-beam directive antenna system, a directive pattern in any plane comprising .a symmetrical major lobe having a narrow half power Width, deep nulls adjacent thereto, and minor lobes of negligible intensity.

It isanother object of this invention to transform a quasi-toroidal wave front into a plane wave front. I

It is another object of this invention to produce, in transmission, a flat wave front and, conversely, in reception, to absorb a maximum amount of energy from an incoming flat wave front, utilizing a concave antenna reflector at least'aportion of which has a parabolic contour. It is still another object of this invention to obtain, in an antenna system comprising a concave passive reflector and an active or primary antenna-therefor, directive radio action comparable to that theoretically obtainable in a hypothetical system comprising a paraboloidal reflector and a truepoint or dimensionless primary antenna at the reflector focal point.

, As used herein the term wave guide generically applies'to conductive guides, such as a 45 two-wire or coaxial line, and to dielectric guides such as a bare, solid dielectric rod or a metallic pipe containing a liquid, solid or gaseous dielectric substance. The term .feed applies broadly to the primary or active antenna, which coopcrates with the main reflector or secondary an,-

tenna, and to th associated dielectric guide; and this term is applicable to receiving, as well as transmitting, systems. In transmission, the feed supplies or feeds the energy delivered by the transmitter to the main reflector, and in reception it supplies or feeds the energy collected by the main reflector to the receiver or other utilization device. Also, as used herein, the term directive characteristic connotes the directive quality, considered in the solid or in three dimensions, of an antenna, whereas the term "directive pattern signifies the trace or projection on a specified plane, such as the E plane or H plane, of the directive characteristic.

In accordance with one embodiment of'thein- 4 the numerals I2, l3 and I4 denoting, respectively, the focal point, the axis and the vertex of the parabola when it assumes a position I5 opposite from position II. The focal points 8 and I 2 lie on the ring focus or curvate focal line 5. As will be explained hereinafter, the distance a between the reflector axis 3 of the main reflector I and the parabola axis 9, or I3, that is, the radius a of the ring focus 5, is critically dependent upon the design of the primary antenna. For purpose of comparison, numeral I6, Fig. 1, and numeral I1, Fig. 2, denote, respectively, the parabolic-contour andlcircular'openifigof a true paraboloidal reflector having an axis "aligned with the vention, an antenna system comprises a parabo'liform reflector having a reflecting surface corre sponding to that obtained by rotating a parabola," and more particularly its axis aboiit a linep'ar'ah" lel to the parabola axis and herein'ter medithe reflector axis.

cumferential line; and this focal line or focal circle is included in a plane extending perpen dicular to the reflector. axis. The primary antenna for the reflector comprises a wave guide having an annular aperture positionedon, that is, coincident with, the circular focal line. In operation, the E and H plane major lobes are substantially the same, and very "sharp, and the minor lobes are negligible.

The invention will be more fully understood from a perusal of the following specification taken in conjunction with the drawings on which like reference characters denote elements of similar function and on which: 7

Figs. 1 and 2 are, 'respectively,'side sectional and'front views of "one embodiment of the invention;

Fig. 3 illustrates the measured directive patterns for the primary antenna inthe embodiment of Figs. 1 and 2;

Fig. 4 illustrates the directive patterns for the 7 complete embodiment of Figs. 1 and 2;

Fig. 5 is'a perspective view'of another embodi-c' merit of the invention;

Fig.6 "illustrates the directive patterns forithe. embodiment Of'Fig. 5; and y Fig. 7 illustrates, for comparison purposes, "the directive patterns of acomparable prior art antenna comprising a conventional parab'oloidal 'reflector and "a front disk reflector. 7

Referring to Figs. 1 and 2, reference "numeral I denotes a concave main reflectorhaving a vertax 2, a reflector axis '3, jacircul'ar opening 4 and a circular or circumferential 'foc'a'lline 5, that is, 'a focal circle or ring focus 5. The 'refl'ec'tor' I has a flat central or inner portion 5 'andanouter parabolic surface l and hence, in any "plane containing axis 3, its contour or configuration is paraboliform. In general, "the surface of reflector I corresponds 'to that obtained by rotating the axis of a parabola, 'and'the parabolic curve portion lying on one side'of the parabola axis, about a given line parallel 'to the parabola axis, and in a manner such that'the axisof'the parab- 01a rotates about the line andjgen'erates a cyl inder, Thus, in Fig. 1, reference numerals 8, 9 and I ll denote, respectively, the 'focal 'po'int, the axis and the vertex of a parabola', thefupper portion of which is represented by adash-dash line II and the lower portionpf which coincides with the lower portion "of reflectorfl tenet-at ing the parabola about the' axis 3 f' frefle'ctor I a 'paraboliform"suifaceis generateii' orobtained; 75 se -seam in es'isuremeiit that zwave xtent The focus of the'parabolifoi'm" reflector is a circular, or more accurately. a. cir 7 axis 3 of the paraboliform'reflector I.

: Reference numeral I8 denotes a translation deyice such as a radar transceiver and numeral I9 designates a dielectric circular guide comprising a metallic tube"!!! containing a dielectric 2I (air) and having an outside radius band an inside radius '0. The guide I9 extends through the vertexportion fi of reflector I and along the reflectori axis 3. It is connected at its near end to device l8, and a circular iris or opening 22 of radius c is provided atfits far end. Numeral 23 'denotes 'a metallic cup or drum having a depth or-axial length d'and'comprising'a cylindrical Wall or rim 24 and a circular disk reflector 25 attached thereto andhavinga radius e. In practice, the wall. and disk 25 are preferably formed from one piece'of sheet metal. The disk 25faces both aperture 22-and the-main reflector I; The guide I9 projects into thedrum 23 a distance i "and forms with the outer surface of guide Man annular antenna aperture 26. A streamline housing "(not shown) 'of-electrically transparent nia-v teria'lencloses the drum 23 and antenna aperture 26' and rigidly secures the "drum primary antenna to, guide I 1 I The-axial spacing between the disk 25 and the iris '22,'and the radial spacing between guide I9 and the rim 24 are denoted, respectively, by the reference letters g and h. The circular iris 22,

. the circular disk '25, the annular antenna aperture 26 and the ring focus5 are coaxially related and :centered "onthemain'reflector'axis 3. The radius ;a :of the 'ring'focus '5 is greater than-the radiusc of iris llandsinalli than the-radius'e *ancewith Fig. 1 and tested at an operating or de- 7 sign wavelength 1% equal to 3 tent-meters, as discussedbelow iirconn'ection with Figs. 3 and 4,-th'e dimensions a, b,ic, -d, e,f,"g,'h and i'wereapproxi mat'ely 0.64%, 0.33).,"0;30 .,0.'66X, i.0 0.29 0. 37)., 0.66). and -0;I65 \,'respectively; f- "In operation, Figs. 1 and '2, "assuming flevi c'e' l-B is ar'a'dar transceiver, mici'iiwave's supplied 'by the transmitter infdevic'e 18 are conveyed ever guide 19 andemitted attire "iris 22. The waves impingin gupon the disk refl'ee'tor 2 5 and refl'ect'e'd thereby'pass through'the annular antenna a' er ture-26am illuminate o'r "energii'e the entire con: eavemaih reflector; and are thence propagates primarily in the ection Tl alig'ned with the reflector axis 3. In reception, thecbnverse bperatio'nf is obtained, and the incoming echo waves impinging u onf refieeter are directed into the amines an thence *eonveyeu ever guide 19 to th reeeiver and indi tor indevicm.

; Consideredin-mo edetailfappli-canthas' found established by the primary antenna 26 in any ,plane containing the reflector axis 3 may be expressed in cylindrical coordinates by the equation ':r -l-'(;o-0L) =r (1) where a and r are constants and :1; and p are cylindrical coordinates. See Elements of Analytic Geometry, by P. E. Smith and A. S. Gale, page 394.

With 1' Incidentally, when the line mentioned above does not pass through the section, that is, when a is larger than 1', the surface generated is the same as that of the well-known toroidal or doughnut-shaped coil. Hence the wave front, considered in the solid or in the three dimensions, produced by the annular antenna aperture 26 is quasi-toroidal with an apparent origin coincident with the circular focus 5. For a drum primary antenna, such as the drum 23 which produces, as explained above, a quasi-toroidal wave front, the proper concave reflecting surface, for optimum gain and an optimumpoint-beam, is given by the equation 7 a) =4Fa: (2) where F is the focal length of the reflector, and a is a constant and, as stated above, is the radius of the ring focus 5. See page 179 of the textbook mentioned above. 1-,

-. ..Equation 2. represents the surface generated by a parabola rotated about a :line parallel to its axis at a distance a from the axis. Hence, in accordance with the invention, a paraboliform reflector I having a ringifoc'us is utilized. with'a primary antenna which produces or receives a quasi-toroidal wave front, the ring focus and the apparent origin of the quasi-toroidal front being coincident. The radius a of the 'ring focus, and therefore the relative areas of thevertex portion and outer portion of reflector I, are determined by the design or size of the primary antenna 26 and, in particular, by the radius of the circular origin of the quasi-toroidal wave front. In the embodiment of Fig. 1, the radius of the circular origin corresponds to the mean radius of the annular antenna aperture 26.

Referring to Fig; 3,-reference numerals 28 and 29 denote, respectively, the measured directive zero or E plane pattern and the measured 90- degree of H plane pattern, of a primary antenna 26 of the drum type, as shown in Fig. 1, the drum dimensions being as given above. While the E plane may have any position, during the test it was horizontal. Reference numeral 3!) denotes the directive pattern taken in the 45-degree plane bisecting the dihedral angle formed by the E and H planes and hereinafter termed B plane. Reference numerals 3!, 32 and 33 denote, respectively, the major lobes of patterns 28, 29 and 30. As shown in Fig. 3, the three patterns are substantially the same so that the major lobes or beam, considered in the solid, is symmetrical about the axis 3 of reflector l. Because of the unavoidable presence of the guide l9, each major lobe is bifarious or bicephalous and includes a cone-shaped core or axial region 34 of null action. Since the guide I!) extends between the primary antenna 26 and the secondary antenna I, and is aligned with the beam core, the cone of null action is not significant and the entire reflector I is adequately illuminated. The lobe, "it will be .noted, tapers from a maximum intensity value in the axial region to a value about 10 decibels below maximum at degrees whereby optimum illumination is obtained as explained in myPatent 2,422,184 mentioned above. ,1 I

In Fig. 4, reference numerals 35 and 36 designate, respectively, the E plane and H plane measured patterns of a complete system, such as illustrated by Fig. 1, and comprising a main paraboliform reflector having a ring focus and a primary antenna of the drum type. The E plane pattern v35 includes a major lobe 31, the first nulls 38, the first minor lobes 39 and the secondary minor lobes 4B; and the H plane pattern includes a major lobe 4|, the first nulls 42, the first minor lobes 43 and the secondary lobes 44. As shown,

:theiportions of major lobes 31 and' li 'abovelO decibels are exactly superimposed, and the portions below 10 decibels are almost exactly superimposed; so' that a point-beam having, as is desired, equal E plane and H plane widths is secured, The'half power width of the major lobes 31, 4|, taken at'the -3 decibel point, is about 4.8 degrees and the axial gain is 31.3 decibels. Also, as is desired, the E plane and H plane first nulls 38, 42 are down atleast 30 and 30.5 decibels, respectively; and the E plane and H plane first minor lobes 39, 43 are down at least 21 and 18.5 decibels, respectively.

The system of Fig. 5 is the same, from a structural standpoint, as the system of Figs. 1 and 2 except that a disk reflector 25 is utilized in place of the drum 23, that is, the wall 24 is omitted in the system ofFig. 5. v The disk reflector '25 is attached to the guide l3 by means of the electrically transparent housing 45. In Fig. 5, the ring focus is between the disk reflector 25 and the end iris 22 in guide l9, whereas in Figs. 1 and 2, it is between the main reflector I and the end iris 22. In one tested embodiment of Fig. 5, the spacing g between the disk 25 and the end iris 22 of guide l9 was 0.331, as compared to g=0.37 for the tested embodiment of Figs. 1

and 2; and the radius a of the ring focus was 0.571 as compared to 0.631 for the tested. system using a drum 23. Also, in the tested embodiment of Fig. 5, the spacing between the disk 25 and the ring focus was 0.13) and the radius e of the disk 25 was 1.0x, as in the tested embodiment of Figs. 1 and 2.

' The transceiving operation of the embodiment of Fig. 5 is substantially the same as that -'-of the system of Figs. 1 and 2. The disk primary antenna 22, 25 of Fig. 5 produces a quasi-toroidal wave front which differs to some extent from the quasi-toroidal wave front established by the drum primary antenna 22, 25, 26 of Figs. 1 and 2. Also while the directive patterns (not shown) of the disk primary antenna are of the point-beam type, they are not in general as satisfactory as the point-beam patterns shown in Fig. 4 and obtained for the drum primary antenna of Figs. 1 and 2; and accordingly the drum primary antenna of Fig. 1 is preferred over the disk primary antenna of Fig. 5.

Referring to Fig. 6, reference numerals 46 and 41, denote, respectively, the measured E and H plane directive patterns for a system similar to that illustrated by Fig. 5 and comprising a paraboliform secondary antenna l and a disk primary ainan-ta parstoieidai-refieetor I6, t! tries; 1' and-sienna 7 minor lobes 39; and the =-H= pianepatterns 4 41 -(F-i g;-'6)and'49 (Fig. eacti inol'uele a. major lobe 4 I the fi'rst nulls '42 and the-first minor lobes fl. Comparing the E plane patterns fi (Fig.1 6-) and $18 (Fig. 8) foi' the systemof the invention, Fig; :5, and the coinparable prior art 'system; it will be seen that th'e first'min'or lobes 139., Fig; 6, ior t'he system or the invention are at :least -18 :decibels down "and therefore relatively-1 10M as :gie'sired, whereas 'thefirst im'no'r lobes 3!, Fig.1? for the prior art system; are only about -12 decibels down. In the plane, thefirst minor lobes-'43,- Figs; 6 and =7, "of the two systems have about the same intensity, s== 19' decibels; The B plane-minor lobes 3-9, 'F-ig'.- 7, are very close-to the major lobe 31 and in effeet form withthe major'lobe 3! a very wide main lobeat thee-12 decibel point, whereby the upper portions of the E and H plane main lobes,-Fig.' 7, for the prior art systemare substantially diiTeren-t and-a true point-beam, considered in the solid, is not obtained. On the other-hand, the E and H plane major -lobes 3l, M, Fig.- 6, for thesystem of the invention are substantial-ly'the 'same down to the 18 decibel point, and a highly satisiactonypointbeam is secured. As indicatediin the Figs. fi-and 7, the :gain of-the system ofthe inventionis about decibel greater than thegain of the prior-art system. 7

As is apparent froma comparison of Figs; 4 and 7-, the patterns :35 and 36' for the system of .1,

comprising a drum type primary antenna are {greatly superior to those of -the prior art system. Thus,rinFig. '4 the major lobes 3 1 and -4-l-have equal half power widths and are exactlysuperimposed,-sothat an excellent point-beam obtamed; whereas in :Fig. .7 the plane major lobe -31 is-wider than the -E plane major =l-obe-4-l.- The firstmulls 3-8, M. in Fig; 14 are-much deeper than these in :Fig. --7 and the E .planetminor lobes fl, Fig; M 4, are much lower-than the corresponding 8 4. 'mthough-th intentien has b'eenexplained in "connection with ee'rtain' embodimentsit is to 'b'e understood'that it is not'to be'limited to theembodiments described-inasmuch as other apparatus may be employed in successfully practicing the invention.

What is claimed is? V e 1. In combination; a concave- 'm'ain'refiector having an axis and a focal circle, said focal circle being-included in *a "plane perpendicular to' and centered on said} axis; a dielectric guide extend-'- the vertexof said 'rei'iecto'r and along "said axis,-'sai i'l guide {having an end circularap'erturey'anda flatciroular reflector facing said apef- "tureand said main reflector,- th'e diameter of said feealbimle being greater thanthatof said circular aperture and-smaller than that of said eireular research 7 v 2. In oombinejtion; a paraboliform main -'reneeter having s :foeal ci-fle; a cireifi'ardilectrio uide-extending' through the vertex-of-said re"- sminor lobes in-F-i-g.17. The-gain 31B decibels :for

the system of Fig. 1 is 3113 decibels whereas'the gain for the prior art system-isaboutaofi decibels. Hence, as compared to the'eprior art-system, the antenna systems of the invention have a higher gain-. lower m-inor-lobes, and-more-desirable pointbeams.-- e

fiectoi' andfl'iavin 1 an end circular iape'i turey a drum-reflector eo-m'prising a cylindricai wall and a eircular disk reflector attachedto said wall and :faoin'gsaidaperture; the 1 151211111151381 "-Of Said 1 01385 biicl' bei h'giintrmediateto the diameters 0f said drum-reflector:and said-aperturel 1 a 3. A combination"in aceordance with ciaimszz, 7

said guide extending into said drum reflector and forming therewithian annular antenna aperture aligned'oreomcidentwith'said focal circle? 7 "C AS'SIU'S CUTLER V REFERENCES cL'rEnL: l e

. v The following re'rerenoes am of record inihe file of this-patent: a.

I UNTIEDSTAFIES Number: Name 7 Date? I 40 1281;752 Baileyauaast. .l .l- Oct. i=5; 1.95.8 1;857,120- IT-raI1Sci1i11 May 3,1932 l,'9 I3;296 Schroter Sept. 1-1,:1934 -2;083 ,242 Runge June 8, 19.3.7 $095,083 Benoit-11s.--- -s 0017-, 15, ==:1,9.3-%7 .i2,206,-923 Southworth July 9, 1 940 -'2,37.0,-053'- Lindenblad s. Feb. 20911945 12,407,05 Carter: Sept. ii-Q1946 2,422,184 Cutler as. o June- 17;, 194i I 00 Number Country 'Date sz' zisos France -r. sr s s --Nok/, 3,4921

1394,423 Germany sin-le s, July 4,. 1910 

